AB0984 CHANGES IN PLASMA VOLUME WHEN MEASURING BIOCHEMICAL MARKERS OF JOINT TISSUE TURNOVER IN RELATION TO ACUTE PHYSICAL ACTIVITY
Authors: J. Bjerre-Bastos, C. Sejersen, H. B. Nielsen, N. Secher, C. C. Kitchen, C. P. Miller, A. Mackey, A. R. Bihlet
Journal: Annals of the Rheumatic Diseases (2022)

Background Physical activity can induce acute changes in plasma volume (PV) and thereby influence concentration of plasma constituents, such as biochemical markers 1,2 . However, it remains undocumented to what extent PV changes occur during physical exercise in osteoarthritis (OA) patients. Objectives Investigating the direct course and magnitude of PV changes during and after weight-bearing (WB) and non-weight-bearing (NWB) exercise, adrenaline-induced cardiovascular stress and resting in an OA population. Methods Data originates from the EFEX-OA-02 study (Reg. no.: NCT04542668 ), which explored biomarker changes in knee OA patients during and after running, cycling, adrenaline infusion and resting on separate days. Blood samples were obtained before, during, at five time points after and again 24 hours post exercise/infusion. Hemoglobin (Hgb) and derived hematocrit (Hct) were measured at all time-points to monitor PV fluctuations. Main inclusion criteria: Cumulative Kellgren-Lawrence (KL) radiographic grade of the left and right knee of ≥ 2, 40-75 years of age, bodyweight 50-100 kg and BMI 18.5-35.0 kg/m 2 . Active interventions consisted of 4x5-minute intervals each progressing from low intensity and peaking at ≥80% of the heart rate reserve (HRR). For the adrenaline infusion, 0.06 mg/kg of adrenalin was prepared in 50 mL saline and administered intravenously. At rest, blood samples were collected at time points similar to the other study interventions, however the 24-hour follow-up sample was omitted. Hgb was measured on a ABL800 FLEX blood gas analyzer and converted to Hct using the formula: Hct (%) = (0.0485 × c tHb (mmol/L) + 0.0083) × 100. Estimated PV change (% ΔPV) was calculated as: % ΔPV = [100 / (100 – Hct pre )] x [100 (Hct pre – Hct post ) / Hct post ], where: ΔPV % = Percentage change in PV: Hct pre = Hct before exercise, Hct post = Hct after exercise. A repeated measures linear mixed-model and 1-way ANOVA was used to assess PV changes and compare interventions, respectively. Results Forty subjects were included. Mean age was 60.4 years (Standard deviation (SD): 8.7), 16 (40%) were male, mean BMI was 27.0 kg/m 2 (SD: 3.5), and mean score in the nine item pain domain of the Knee Injury and Osteoarthritis Outcome Score (KOOS) at baseline was 67.5 (SD: 15.2) out of 100 (0 and 100 corresponding to max pain and no pain, respectively). Baseline Hgb was 9.05 mmol/L (SD: 0.68) and Hct was 44.7% (SD: 2.9%). All subjects were able to reach the defined peak cardiovascular intensity or higher during exercise, while reaching on average 70% (SD: 8.7%) of that during the adrenaline infusion. Cycling, running and adrenaline infusion led to acute reductions in PV compared to rest: Cycling -14.3% (95%CI: -10.0 to -18.7%), running -13.9% (95%CI: -10.9 to -17.0%), adrenaline -7.8% (95%CI: -4.2 to -11.5%). The reductions in PV induced by both cycling and running were greater compared to adrenaline (p&lt;0.001). There was no difference in PV changes after cycling vs. running (p=0.99). Thirty minutes after both modes of exercise, PV had returned to baseline. After completion of the adrenaline infusion, PV returned to baseline at 30-60 minutes, but was lower than baseline levels at 120 minutes by -3.9% (95%CI: -0.7 to -7.1%), at 240 minutes by -5.3% (95%CI: -2.1 to -8.6%), and at 24-hour by -5.9% (-2.0 to -9.9%). During seated rest, PV initially increased (3.1%, 95%CI: 0.7-5.4%) (Figure 1). Conclusion Moderate-high intensity running, cycling and cardiovascular stress led to rapid reductions in PV of knee OA patients. Adjustment for PV changes should be considered when measuring biochemical markers in relation to physical activity. References [1]Kaltreider NL, Meneely GR: THE EFFECT OF EXERCISE ON THE VOLUME OF THE BLOOD. J Clin Invest, 1940. [2]Novosadová J: The changes in hematocrit, hemoglobin, plasma volume and proteins during and after different types of exercise. Eur J Appl Physiol Occup Physiol, 1977. Disclosure of Interests Jonathan Bjerre-Bastos: None declared, Casper Sejersen: None declared, Henning Bay Nielsen: None declared, Niels Secher: None declared, Carl-Christian Kitchen: None declared, Claire Prener Miller: None declared, Abigail Mackey: None declared, Asger Reinstrup Bihlet Employee of: Full-time employee of NBCD/Sanos Group A/S